The increasing reliance on communication networks to transmit more complex data, such as voice and video traffic, is causing a very high demand for bandwidth. To resolve this demand for bandwidth, communication networks are relying more upon optical fibers to transmit this complex data. Conventional communication architectures that employ coaxial cables are slowly being replaced with communication networks that comprise only fiber optic cables. One advantage that optical fibers have over coaxial cables is that a much greater amount of information can be carried on an optical fiber.
The Fiber-to-the-home (FTTH) optical network architecture has been a dream of many data service providers because of the aforementioned capacity of optical fibers that enable the delivery of any mix of high-speed services to businesses and consumers over highly reliable networks. Related to FTTH is fiber to the business (FTTB). FTTH and FTTB architectures are desirable because of improved signal quality, lower maintenance, and longer life of the hardware involved with such systems. However, in the past, the cost of FTTH and FTTB architectures have been considered prohibitive. But now, because of the high demand for bandwidth and the current research and development of improved optical networks, FTTH and FTTB have become a reality.
One example of a FTTH architecture that has been introduced by the industry is a passive optical network (PON). While the PON architecture does provide an all fiber network, it has many drawbacks that make such a system impractical to implement. One drawback of the PON architecture is that too many optical cables must originate at the head end or data service hub due to limitations in the number of times an optical signal can be divided before the signal becomes too weak to use. Another drawback can be attributed to the passive nature of a PON network. In other words, because there are no active signal sources disposed between the data service hub and the subscriber, the maximum distance that can be achieved between the data service hub and a subscriber usually falls within the range of 10 to 20 kilometers.
Another significant drawback of the PON architecture is the high cost of the equipment needed at the data service hub. For example, many PON architectures support the full service access network (FSAN) which uses the asynchronous transfer mode (ATM) protocol. To support this protocol, rather complex and expensive equipment is needed.
In addition to the high data service hub costs, conventional PON architectures do not lend themselves to efficient upgrades. That is, conventional or traditional PON architectures force physical reconfiguration of the network by adding fiber and router ports in order to increase the data speed of the network.
The data speeds in the downstream and upstream directions is another drawback of the PON architecture. Conventional PON architectures typically support up to 622 Megabit per second speeds in the downstream direction while only supporting maximum speeds of 155 Megabit per second speeds in the upstream direction. Such unbalanced communication speeds between the upstream and downstream communication directions is undesirable and is often referred to as asymmetrical bandwidth. This asymmetrical bandwidth places a low ceiling or low threshold for the amount of information that can be transferred from a subscriber to a data service hub. The asymmetrical bandwidth is a result of the high cost of optical components required.
To overcome the asymmetrical bandwidth problem and the limited distance between the subscriber and the data service hub, a conventional hybrid fiber-to-the-home (FTTH)/hybrid fiber-coax (HFC) architecture has been proposed by the industry. HFC is currently the architecture of choice for many cable television systems. In this FTTH/HFC architecture, an active signal source is placed between the data service hub and the subscriber. Typically, in this architecture, the active signal source comprises a router. This conventional router has multiple data ports that are designed to support individual subscribers. More specifically, the conventional router uses a single port for each respective subscriber. Connected to each data port of the router is an optical fiber which, in turn, is connected to the subscriber. The connectivity between data ports and optical fibers with this conventional FTTH/HFC architecture yields a very fiber intensive last mile. It is noted that the terms, “last mile” and “first mile”, are both generic terms used to describe the last portion of an optical network that connects to subscribers.
In addition to a high number of optical cables originating from the router, the FTTH/HFC architecture requires radio frequency signals to be propagated along traditional coaxial cables. Because of the use of coaxial cables, numerous radio frequency (RF) amplifiers are needed between the subscriber and the data service hub. For example, RF amplifiers are typically needed every one to three kilometers in a coaxial type system. The use of coaxial cables in the FTTH/HFC architecture adds to the overall cost of the system because two separate and distinct networks are present in such an architecture. In other words, the FTTH/HFC architecture has high maintenance costs because of the completely different waveguides (coaxial cable in combination with optical fiber) in addition to the electrical and optical equipment needed to support such two distinct systems. Stated more simply, the FTTH/HFC architecture merely combines an optical network with an electrical network where both networks run independently of one another.
Another drawback of the FTTH/HFC architecture is that the active signal source between the data service hub and subscriber, usually referred to as the router, requires a protected environment that occupies a significant amount of space. That is, the conventional router of the FTTH/HFC architecture requires an environmental cabinet that must maintain the router and related equipment at an optimum temperature. To maintain this optimum temperature, the environmental cabinet will typically include active temperature control devices for heating and cooling the cabinet.
Stated more simply, the conventional router of the FTTH/HFC architecture can only operate at standard room temperatures. Therefore, active cooling and heating units that consume power are needed to maintain such an operating temperature in all types of geographic areas and in all types of weather.
Unlike the FTTH/HFC architecture that employs two separate communication networks, another conventional hybrid fiber coax (HFC) architecture employs an active signal source between the data service hub and the subscriber that does not require a temperature controlled environmental cabinet. However, this active signal source disposed between the subscriber and the data service hub merely provides optical to electrical conversion of information signals. That is, the active signal source disposed between a subscriber and a data service hub in the HFC architecture converts downstream optical signals into electrical signals and upstream electrical signals into optical signals. The conventional HFC architecture relies upon coaxial cable to support all signals in the last mile or so of the HFC network. Therefore, similar to the FTTH/HFC architecture, the conventional HFC architecture also requires numerous RF amplifiers on the coaxial cable side of the network.
Another drawback of the conventional HFC architecture exists at the data service hub where numerous communication devices are needed to support the data signals propagating along the optical fibers between the active signal source and the data service hub. For example, the conventional HFC architecture typically supports telephony service by using equipment known generically as a host digital terminal (HDT). The HDT can include RF interfaces on the cable side, and interfaces to either a telephone switch or to a cable carrying signals to a switch on another side.
Further, the data service hub of a conventional HFC architecture can further include a cable modem termination system (CMTS). This system provides low level formatting and transmission functions for the data transmitted between the data service hub and the subscriber. The CMTS system can operate by-directionally, meaning that it can send signals both downstream to subscribers and receive signals sent upstream from subscribers.
In addition to a CMTS, the conventional HFC architecture at the data service hub typically includes several modulators that can comprise miniature television transmitters. Each modulator can convert video signals received from satellites to an assigned channel (frequency) for transmission to subscribers. In addition to the modulators, a signal processor and other devices are used to collect the entire suite of television signals to be sent to subscribers. Typically, in a conventional HFC architecture, there can be 78 or more such modulators or processors with their supporting equipment to service the analog TV tier. Additionally, similar equipment to serve the digital video tier is often used.
Another drawback of the conventional HFC architecture flows from the use of the CMTS. Similar to the passive optical network (PON) discussed above, the CMTS cannot support symmetrical bandwidth. That is, a bandwidth of the conventional HFC architecture is typically asymmetrical because of the use of the data over cable service interface specification (DOCSIS). The nature of the DOCSIS standard is that it limits the upstream bandwidth available to subscribers. This can be a direct result of the limited upstream bandwidth available in an HFC plant. Such a property is undesirable for subscribers who need to transmit more complex data for bandwidth intensive services such as home servers or the exchange of audio files over the Internet.
In another variation of the conventional HFC architecture, the CMTS can be part of the active signal source disposed between the subscriber and the data service hub. While this variation of the conventional HFC architecture enables the active signal source to perform some processing, the output of the active signal source in this architecture is still radio frequency energy and is propagated along coaxial cables.
Accordingly, there is a need in the art for a system and method for communicating optical signals between a data service provider and a subscriber that eliminates the use of coaxial cables and the related hardware and software necessary to support the data signals propagating along the coaxial cables. There is also a need in the art for a system and method for communicating optical signals between a data service provider and a subscriber that supports high speed symmetrical data transmission. In other words, there is a need in the art for an all fiber optical network and method that can propagate the same bit rate downstream and upstream to/from a network subscriber. Further, there is also a need in the art for an optical network system and method that can service a large number of subscribers while reducing the number of connections at the data service hub.
There is also a need in the art for an active signal source that can be disposed between a data service hub and a subscriber that can be designed to withstand outdoor environmental conditions and that can be designed to hang on a strand or fit in a pedestal similar to conventional cable TV equipment that is placed within a last mile of a communications network. A further need exists in the art for a system and method for receiving at least one gigabit or faster Ethernet communications in optical form from a data service hub and partition or apportion this optical bandwidth into distribution groups of a predetermined number. There is a further need in the art for a system and method that can allocate additional or reduced bandwidth based upon the demand of one or more subscribers on an optical network. Another need exists in the art for an optical network system that lends itself to efficient upgrading that can be performed entirely on the network side. In other words, there is a need in the art for an optical network system that allows upgrades to hardware to take place in locations between and within a data service hub and an active signal source disposed between the data service hub and a subscriber.